The Bulgarian authorities responded with outrage on Friday to suggestions by England manager Gareth Southgate that his players anticipated racist abuse when they visit Sofia in Euro 2020 qualifying.
In a statement posted on its website, the Bulgarian Football Union (BFU) said it "views such behaviour as groundless, inappropriate and unnecessary prior to the important and exciting football game that Bulgarian fans have been looking to in the past year".
After a Bulgarian fan was ejected and briefly held by police following the meeting between the countries at Wembley on Saturday, Southgate said racist abuse was a "concern" ahead of the return game next month.
"We're aware that there is history there," Southgate said. "We want to make sure that we're all prepared for what might happen and how we want to respond."
The BFU said their president, Borislav Mihaylov, had written formal letters of complaint to UEFA and the English Football Association "expressing his indignation and disappointment following the public comments by Mr. Gareth Southgate and the suggestions that the English players will be subject to racial abuse by the Bulgarian supporters".
England's Raheem Sterling was reportedly the target of racist language from a fan in Bulgarian section. The fan was ejected during the first half of England's 4-0 victory and handed to the police, before being released.
"It is a concern," Southgate said about the return game. "It's something that we've already planned."
The game will be England's first visit to Bulgaria since September 2011, when Ashley Young was subject to monkey chants as the visitors won 3-0.
The BFU was fined 40,000 euros by UEFA for "discriminatory" chanting and because fans threw fireworks.
Bulgaria were also punished by UEFA for "racist behaviour" when they lost away to the Czech Republic on June 7 and at home to Kosovo three days later in Euro qualifying.
For the England visit, UEFA has ordered the BFU to close at least 5,000 seats at the Vasil Levski National Stadium and display a banner that reads: "#EqualGame".
Friday's Bulgarian statement concluded by acknowledging the possibility of similar abuse when England visit while implying that Southgate's remarks were themselves racist.
"Even if this were the case, however, we believe that generalisations and the creation of needless tension by official members of the English team is absolutely unacceptable and in contradiction with the spirit of mutual respect and fair play," the BFU said.